It is desired to produce magnetic recording media having the highest possible recording density. One technique to achieve this is to orient the magnetic particles in the magnetic media in a direction perpendicular to the plane of the media or to the plane of the substrate to which the media is applied (the Z direction). A conventional method of orienting magnetic particles is to maintain the magnetic coating or paint as it is applied to a substrate in an orienting magnetic field until the paint is sufficiently dried to maintain the particles in the desired fixed position. This presents no serious problem when the particles are aligned in the plane of the substrate because they will not tend to move from the position initially brought about by the magnetic field. However, when the desire is to align or orient the particles in the direction perpendicular to the plane of the film, other forces are involved which tend to cause the magnetic particles to revert to the direction in the plane of the substrate. Thus, either the coating must be maintained within the vertical aligning magnetic field until it becomes sufficiently dried to support the particles in the Z direction or the viscosity of the coating composition must be raised to the point where it will support the magnetic particles even after the removal of the magnetic aligning field until the coating is fixed and will thereby support the particles. In the former instance this is impractical because when a substrate is being coated with a magnetic paint at high speeds, such as speeds running into hundreds of feet per second, the magnetic field would be required over several hundreds of feet even if the coating required only two or three seconds to become dry. The latter technique, that being the increase of viscosity of the coating composition creates problems because as the viscosity increases, it becomes more difficult to align the particles in the desired direction because the forces required are greater.
The difficulty in orienting the magnetic media in the vertical direction is rendered even more severe due to the demagnetization related to this direction. If every particle in the magnetic media, with saturation magnetization of Ms is perfectly oriented in the positive Z direction, the demagnetization field will be 4.pi.Ms pointed in the negative Z direction. A typical value of 4.pi.Ms demagnetization field is about 1000 Oe for cobalt doped iron oxide film. Under such a strong demagnetization field, the magnetic particles in a normal viscous dispersion cannot maintain the vertical orientation outside the magnetic field for more than a few seconds. Therefore, as the coated medium leaves the applied orienting field, the magnetic particles rotate down to the in-plane directions.